Spindle structure

ABSTRACT

A spindle structure in which a noise occurrence due to a tap hole and a screw  2007  is effectively prevented. A nut  8  for adjusting a preload of a bearing  5  is threadedly engaged with an outer circumference of a spindle  2 . On an edge of the nut  8 , a plurality of tap holes for balance adjustment are provided at even intervals on a circumference centered around the axis of the spindle  2  and to be parallel to the axial direction of the spindle  2 . These tap holes are countersinked, and a plate screw  11  is threadedly engaged so that an edge of each plate screw  11  is flush with a surface of the nut  8 . In addition, the plate screw  11  is used as a balance weight by changing the length thereof.

BACKGROUND OF THE INVENTION

This application claims the benefit of Japanese Patent ApplicationNumber 2006-322411 filed on Nov. 29, 2006, the entirety of which isincorporated by reference.

1. Field of the Invention

The present invention relates to a spindle structure of a machine tooletc., and more specifically, to a technology to prevent noise whichoccurs when the spindle rotates in a high speed.

2. Description of the Related Art

Generally, a spindle rotating at a high speed has a tap hole for balanceadjustment on an end surface or has other parts such as a dog fordetecting a position mounted by a screw. Thus, when the spindle isrotated, there is a problem in which an external wind noise occurs dueto the tap hole and a protruding head of the screw. To solve theproblem, as disclosed in Japanese publication of unexamined patentapplication 2000-218465, a cover for covering a rotating portion, or alid for covering the tap hole has been used.

However, a noise reduction effect is small even when the rotatingportion is covered by the cover. Further, the lid protrudes from an edgeof the spindle even when the tap hole is covered with the lid, resultingthat external wind noises would occur due to the protruded lid. Althoughthe entire spindle is usually covered by a cover, an external wind noisereduction effect is small even if the effect of the cover is consideredin addition to the above countermeasures. In other words, it is verydifficult to reduce the noise completely.

In view of the above, an object of the present invention is to provide aspindle structure to effectively prevent a noise occurrence by a taphole and a screw.

SUMMARY OF THE INVENTION

In order to achieve the above object, the invention according to a firstaspect is characterized by a spindle structure in which a plurality oftap holes are provided with a rotating portion for balance adjustment,wherein each tap hole is countersinked, and a plate screw whose edge isflush with a surface of the rotating portion in a screwed state isscrewed into the tap hole as a balance weight where the length of theplate screw is changed.

In order to achieve the above object, the invention according to asecond aspect is characterized by a spindle structure in which otherparts are mounted on a rotating portion by a screw, wherein either of ascrew hole and a penetrating hole defined in the other parts iscountersinked, and the other parts are mounted using a plate screw whoseedge is substantially flush with a surface of the other parts in amounted state.

It should be noted that “a rotating portion” in this invention includesnot only a spindle, but also a draw bar which rotates with the spindleand other components such as a dog for detecting a position.

According to the present invention, the tap hole is covered with theplate screw which does not protrude from a surface of the spindle orother parts. Consequently, when the spindle rotates at a high speed, anexternal wind noise does not occur by the plate screw, so that noiseoccurrence is effectively prevented.

In particular, a simple method where countersinking is added to anexisting tap hole etc. which is covered with a plate screw is applied,so that additional cost will be minimum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanation view of a rear portion of a spindle in amachining center.

FIG. 2 is a detail view of the portion B of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be explainedwith reference to the drawings.

FIG. 1 is an explanation view of a rear portion of a spindle in amachining center, in which a figure in the right is a front view, and afigure in the left is a sectional view taken along the line A-A. Thereference number 1 denotes a housing which supports a spindle 2 so as tobe rotatable via a plurality of bearings 5. The reference number 4 is aspacer provided between the bearings 5,5 and the reference number 6denotes a lid mounted on an edge of the housing 1. A draw bar 3 isassembled into a penetrating hole defined at the center of axis of thespindle 2 so as to be movable in the longitudinal direction. When thedraw bar 3 moves in the longitudinal direction by a not shown anoil-hydraulic cylinder, a not shown tool clamping device performs aclamp or unclamp operation, so that a tool is attachable and detachableto/from a tip of the spindle 2. Moreover, the draw bar 3 has aring-shaped dog 9 on an edge of the draw bar 3, which detects a positionof the draw bar 3 with a proximity sensor 21 and judges whether or notthe tool is mounted on the spindle 2.

As shown in FIG. 2, which is a detail view of the B portion of FIG. 1,the dog 9 has a countersinked screw hole defined at even intervals on acircumference centered around the axis of the draw bar 3 and to beparallel to the axial direction of the draw bar 3. When a plate screw 12screwed into this countersinked screw hole is threadedly engaged with anedge of the draw bar 3, the dog 9 is assembled to the draw bar 3. Inthis assembly state, an edge “a” of the plate screw 12 is flush with asurface “b” of the dog 9.

On the other hand, a nut 8 is threadedly engaged with an outercircumference of the spindle 2, and by adjusting the fastening length ofthe nut 8, a preload of the bearing 5 can be adjusted via a collar 7. Onan edge of the nut 8, a plurality of tap holes for balance adjustmentare defined at even intervals on a circumference centered around theaxis of the spindle 2 and to be parallel to the axial direction of thespindle 2. As these tap holes are also countersinked, all tap holes areengaged with a plate screw 11 to be covered. Here, similar to FIG. 2, anedge of each plate screw 11 is flush with a surface of the nut 8. Inaddition, the plate screw 11 is used as a balance weight by changing itslength.

In the spindle 2 as configured above, the tap hole of the nut 8 iscovered with the plate screw 11, and the screw hole of the dog 9 iscovered with the plate screw 12, respectively. Moreover, since the platescrews 11, 12 do not protrude from a surface of the nut 8 and dog 9, anexternal wind noise due to the plate screws 11, 12 does not occur, evenwhen the spindle 2 rotates with the draw bar 3 at a high speed.

In this way, according to a spindle structure in this embodiment, eachcountersinked tap hole is engaged with the plate screw 11 so that anedge of the plate screw 11 is flush with a surface of the nut 8 in afastened state. Here, the length of the plate screw 11 is changed andthe plate screw 11 is used as a balance weight. In addition, a screwhole defined in the dog 9 is countersinked and the dog 9 is fixed by theplate screw 12 so that an edge of the plate screw 12 is flush with anedge of the dog 9. Thus, noise occurrence is effectively prevented.

In particular, a simple method where countersinking is added to anexisting tap hole etc. which is covered with a plate screw is applied,so that additional cost will be minimum.

Although a tap hole for balance adjustment is provided with a nut to bethreadedly engaged with the spindle in the above embodiment, the taphole may be directly provided with the spindle. Moreover, a screw holescrewed by the plate screw, in this embodiment, is provided with thedog, and in a structure where other parts, a dog for example, ispenetrated by a screw to be screwed into the spindle, a penetrating holeprovided with other parts may be countersinked.

Moreover, it is not necessary that an edge of the plate screw should beexactly flush with a surface of the spindle or other parts, and may beslightly protruded or recessed as long as occurrence of an external windnoise is prevented.

In addition, the present invention is not limited to a machining center,and may be applied to other machine tools. Other than machine tools, thepresent invention may be applied to any machine as long as it has aspindle which rotates at a high speed. Although the present inventionemploys both inventions where a tap hole for balance adjustment iscountersinked to use a plate screw, and where a screw hole or apenetration hole for other parts is countersinked to use a plate screw,only a corresponding invention may be employed in case of a spindle haseither the tap hole or the screw hole etc.

1. A spindle structure in which a plurality of tap holes are provided with a rotating portion for balance adjustment, wherein each tap hole is countersinked, and a plate screw whose edge is flush with a surface of the rotating portion in a screwed state is screwed into the tap hole as a balance weight where the length of the plate screw is changed.
 2. A spindle structure in which other parts are mounted on a rotating portion by a screw, wherein either of a screw hole and a penetrating hole defined in the other parts is countersinked, and the other parts are mounted using a plate screw whose edge is substantially flush with a surface of the other parts in a mounted state. 